Are there be any major firewall issues in multiplayer gameplay?
Few if any. We took our knocks in RoN and learned our lesson and now we’re coming back with one of the greatest multiplayer interfaces available, and using UDP to minimize any troubles with firewalls. Even with a restrictive firewall, you’ll only need one port open, and chances are that if your firewall already allows you to play WC3 online it will allow you to play RoL online.